| Due to the diversity of manufacturing materials and the complexity of operating environment,rail transit vehicles often need protection coatings.Solvent based epoxy/polyurethane coating systems are widely used because of its excellent performance,but a large amount of volatile organic compounds（VOCs）emitted in the coating process pollutes the atmospheric environment.The hydration of epoxy/polyurethane coating can improve the environmental protection performance,and at the same time maintaining the mechanical properties,anti-corrosion performance,application performance and decoration performance of the coating.It is an important research direction for the development of green of coating for rail transit vehicles.According to the performance requirements of rail transit vehicles application,the waterborne epoxy/polyurethane coating system was designed and prepared in this work.The properties and the curing reaction kinetics of coating were evaluated from the four aspects of mechanic performance,anti-corrosion,application and appearance.The influencing factors of coating curing reaction rate and the action mechanism of additives were studied,providing theoretical guidance for the coating process.A waterborne epoxy primer suitable for rail transit vehicles was prepared by optimizing the type of waterborne epoxy resin and the equivalent ratio of reactive groups.Adding scale functional filler and silane anchoring agent can react with hydroxyl groups on the substrate and epoxy resin.The results show that the waterborne epoxy primer has excellent mechanical properties and anti-corrosion properties:the adhesion strength on aluminum alloy substrate reaches 7.51 MPa,which exceeds the requirement of high-speed EMU≥4.00 MPa;The salt spray resistance test reaches 1500 h,exceeding the requirements of rail transit industry for1000 h.At the same time,the effects of Microarc oxidation（MAO）treatment and silane coupling agent surface modification on the improvement of mechanical properties and anti-corrosion properties of waterborne epoxy primer coating were also studied on 7N01 aluminum alloy used for traction beam with higher reliability requirements.It is found that these methods can significantly improve the mechanical properties of the coating.The prepared amphiphilic Linear-Dendritic carbosilane Block Surfactant（LDBS）is introduced into the waterborne polyurethane intermediate coating.The branched lipophilic end of LDBS can spread and adsorb on the surface of polyisocyanate droplets to form physical isolation between water and polyisocyanate and inhibit the side reaction of CO2gas between them,the Bubble Free Film Thickness（BFFT）of two-component waterborne polyurethane coating in the film-forming process increased from 80μm to 120μm,and the effectiveness of LDBS in inhibiting side reactions was confirmed by infrared spectroscopy.In addition,the relationship between the drying time ti of waterborne polyurethane intermediate paint and the parameters of application ambient temperature Te,relative humidity W and wind speed S was studied.The mathematical equation between the drying time and these parameters was established by using the statistical analysis software SPSS,which is suitable for the prediction of drying speed of waterborne polyurethane intermediate paint under different temperature,humidity and ventilation.The accuracy is 93.75%with error less than 10.0%,It can provide guidance for engineering application.The reaction degree between hydroxyl and isocyanate in the film-forming process of waterborne polyurethane topcoat was characterized by infrared tracking method.The effect of cosolvent propylene glycol diacetate（PGDA）on the chemical reaction rate between hydroxyl and isocyanate group was studied,the underlying mechanism was analyzed and discussed by using the collision theory of Max Trautz and William Lewis and Houghes Ingold rule.It is found that when the addition amount of PGDA is about 10%,the synergistic diffusion effect is equivalent to the solvent effect,and the crosslinking curing reaction is the fastest.The effect of leveling agent on gloss and recoating property of waterborne polyurethane topcoat was studied.It was found that the introduced layer shifting leveling agent can effectively improve the gloss of multiple coating topcoats without affecting the interlayer adhesion（recoating property）of topcoats.The mobility of layer shifting leveling agent was characterized by XPS.By introducing nano-oxides,the weather resistance of waterborne polyurethane topcoat is improved through absorption and scattering of ultraviolet rays.After 1500 h artificial climate accelerated aging test,the coating can still maintain good luster,which is better than organic ultraviolet absorber（1000 h）commonly used in rail transit industry.The practical coating experiments were carried out on the 600 km/h high-speed maglev vehicle by using self-prepared waterborne epoxy primer,waterborne polyurethane intermediate paint and waterborne polyurethane finish.The key process parameters are designed,especially the drying temperature and humidity requirements of waterborne polyurethane intermediate paint and finish paint（good ventilation with surface wind speed of about 2 m/s,temperature of 25±5℃and relative humidity lower than 70）were determined.The basic properties such as adhesion strength and gloss of the composite coating of coated vehicles were tested and found to fully meet the application requirements of rail transit vehicles.In addition,the coating of the developed waterborne coating on the carbon fiber composite substrate is explored and studied.It is found that the adhesion strength of the waterborne epoxy primer coating on the polished carbon fiber composite substrate can reach 7.46 MPa.At the same time,the effect of silane anchoring agent on improving the adhesion strength of waterborne epoxy primer on carbon fiber composites was studied.It was found that the adhesion strength of waterborne epoxy primer without silane anchoring agent was only 3.52 MPa,which failed to meet the requirements of rail transit industry,indicating the effectiveness of silane anchoring agent in improving the adhesion strength of carbon fiber composites coating. |
PDF Full Text Request